Machinability of C/C-SiC Ceramics for Components in High-Temperature Applications

Abstract

Ceramic matrix composites (CMC) are trendsetting materials in the aerospace industry. The high-performance CMC materials are suitable for high-temperature applications, e.g. in CO2-saving aircraft turbines. Fiber-reinforced ceramics are characterized by corrosion resistance, temperature resistance, abrasion resistance and a quasi-ductile behavior. However, these properties are challenging in machining operations regarding the process step of finishing. The manufacturing route via a fiber-reinforced plastic (FRP) green compact and a subsequent pyrolysis enables complex geometries and near-net-shape components to be manufactured. But this does not eliminate the need for the finishing process after the liquid silicon infiltration (LSI). Different manufacturing strategies for the production of complex, accurate workpieces include the premachining of blanks in green condition and the challenging finish machining after the ceramization of the material.

The workpiece samples of C/C-SiC ceramics were generated using a green compact out of carbon fiber reinforced polymer (CFRP) with defined fiber orientation for different orthotropic material properties. Machining tests formed the basis for the systematic development of the finishing strategy using cutting tools. These tools are intended to replace the currently established, conventional grinding operations with PCD/ PCBN tools and are supposed to provide an increase in productivity in the manufacturing process.

The goal here was to develop a stable milling operation for CMC materials. For this purpose, scientific fundamentals were worked out for free orthogonal cutting and milling operations. Different concepts for cutting materials and coatings were examined for the reduction of cutting edge wear. Special attention was paid to the wear behavior during the first few cuts of the tools. Hence, the investigations made an important contribution to the future development of tools with complex cutting geometries for the machining of ceramic composites.

Keywords: ceramic matrix composites; cutting tool; wear; milling